1. Field of the Invention
The present invention relates to the generation of windshear models and more specifically to the simulation of microburst windshears for use in research and development of windshear detection equipment for use on aircraft.
2. Description of the Prior Art
Windshear is a weather phenomenon which results in rapidly changing wind velocity o direction and in terms of aircraft flight performance is dangerous during the take off and landing phases of flight. Of the causes of windshear, the microburst has been identified as the most hazardous to aircraft. Several severe aircraft accidents have been attributed to the microburst, the most recent being the crash of a Lockheed L-1011 aircraft at the Dallas-Fort Worth International Airport on Aug. 2, 1985.
The avionics industry is currently in process or has already developed windshear detection systems for installation on aircraft to alert the flight crew of a microburst encounter. One such system is described in U.S. Pat. No. 4,593,285 entitled "Windshear Detection and Warning System with Evasion Command," issued June 3, 1986, and assigned to the assignee of the present invention. In the development of such systems, it is necessary to generate a simulated environment that creates winds similar in nature to those known to exist in actual microbursts. These simulated microburst winds are then used by the windshear detection system to establish thresholds of wind magnitudes or rates at which it is prudent to provide a warning of rapidly changing winds.
In the prior art, these simulated winds were generated in a number of ways. One method changed the wind magnitude as a function of altitude above the ground. In this scheme, as the aircraft climbed after take off, the wind would therefore change. Similarly, as the aircraft descended toward the ground as in the case of a landing, the wind would also change and thereby create a windshear. This scheme is unrealistic, however, in that no windshear would be generated should the aircraft maintain a constant altitude. In an actual microburst encounter, the winds may change both with altitude and distance travelled.
Another scheme used was the changing of winds as a function of the distance travelled along the ground. While this scheme eliminates the problem associated with constant altitude flight, it is also unrealistic in that the wind velocity is identical at all altitudes.
The scheme most in use today for the testing of windshear detection systems is one utilizing predetermined windshear tables in which winds are defined as a function of both altitude and distance. In this scheme, a finite number of points defined by both a distance and an altitude, typically on a grid arrangement, are used. At each point, the magnitudes of orthogonal winds are defined; that is, a horizontal wind magnitude is defined, a horizontal wind 90 degrees to the first is also defined, and finally a vertical wind is defined. In this manner, wind "fields" are thus established. An example of such a scheme may be found in the Federal Aviation Administration's Advisory Circular AC-120-41, entitled "Criteria for Operational Approval of Airborne Windshear Alerting and Flight Guidance Systems".
While the latter scheme is the most realistic of the prior art schemes in terms of generating simulated microburst windshears, it is, in general, cumbersome to use and requires substantial storage capability to define the large number of grid points necessary to establish the wind field. In addition, the wind field so described is unique to a particular microburst model. Consequently, a large number of such wind fields is necessary to adequately test a windshear detection system. This, of course, requires even more storage capability and complexity.
The present invention overcomes the shortcoming of the prior art by establishing a method of simulating microburst winds through the use of four or more vortex models. Each vortex model may be individually increased in strength, displaced relative to the other vortex models, and varied in altitude above the ground. This versatility permits the generation of an infinite number of microburst models and, in addition, allows the creation of microburst models similar to those encountered in actual aircraft accidents. Furthermore, since algorithms are used to determine wind magnitudes, rather than defining a fixed magnitude at a given location, storage requirements are greatly reduced.